1. Field of the Invention
This invention relates in general to magnetic transducers for transferring information signals to and from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. The MR sensor operates on the principle that the resistance of the read element is a function of the amount and direction of magnetic flux being sensed by the element.
The prior art also teaches that in order for an MR element to operate optimally, two bias fields should be provided, a first bias field along its transverse direction as well as a second bias field along its longitudinal direction. The transverse bias orients the magnetization at some skew angle relative to the sense current, as is necessary to obtain a linear component of response to the flux field in the otherwise quadratic response. This bias field is normal to the plane of the magnetic media and parallel to the surface of the planar MR element. The longitudinal bias has the purpose of inducing a single domain state of magnetization, as is required for the suppression of Barkhausen noise. The longitudinal bias field extends parallel to the surface of the magnetic media and parallel to the lengthwise direction of the MR sensor.
One type of bias method disclosed in the prior art is current induced bias in which a parallel auxiliary current produces a transverse bias field on the MR sensor strip. U.S. Pat. No. 3,813,692 shows one example of this bias method. Alternatively, the field from the sense current magnetizes a proximate soft magnetic "keeper film" whose stray field, in turn, exerts a transverse bias upon the MR sensor as is described in U.S. Pat. No. 3,864,751.
Another type of bias method is current deflection bias, as shown in U.S. Pat. No. 4,280,158. Here, the quiescent magnetization remains along the longitudinal direction, while, instead, the sense current is deflected to flow askew to the magnetization. This effect is achieved with a superpositioned "barberpole" conductor configuration. This method produces a transverse bias condition along with a small (typically insufficient) longitudinal bias field underneath the conductor.
A further type of prior art bias method comprises permanent magnet bias in which the bias condition is produced with a proximate hard magnetic film. The hard magnetic film may be ferromagnetic and coupled magnetostatically to the sensor as shown in U.S. Pat. No. 3,840,898. Alternatively, the film may be antiferromagnetic and coupled to the sensor via an exchange mechanism as shown in U.S. Pat. No. 4,103,315. Either method can, at least in principle, provide a transverse and/or a longitudinal bias component.
U.S. Pat. No. 4,418,372 discloses a magnetic rotary encoder comprising a substrate having a surface opposite to a rotary body having plural pieces of magnetic information recorded on at least one circumferentially running track. The substrate has a magnetoresistive element formed on its surface having a pattern including at least two portions extending in the radial direction of the rotary body and connected at the ends by a circumferentially extending portion. The disclosed arrangement is not designed to produce a bias in the MR element, but to produce an additive signal from each of the portions in the radial direction and phasing produced by the circumferential portions.
The prior art bias methods have been effective to meet prior art requirements, but the additional structure required adds complexity to the MR read transducer which it is desirable to avoid. The prior art does not disclose a bias method to provide transverse as well as longitudinal bias solely through the use of a particular MR sensor geometry.